Apparatus and method for measuring detonation velocities in explosives



Sept. 15, 1970. T. Q. CICCONE ETAL 3,528,28Q

APPARATUS. AND METHOD FOR MEASURING DETONATION.

VELOCITIES IN EXPLQSIVES Filed NOV. 27, 1968 Fig./

c; LA EXPLOSIVE BODY 1B 1 /3 [INVENTORS James F; Kowalick Thomas 0.; Ciccane 3 ATTORNEYS.

United States Patent Office 3,528,280 APPARATUS AND METHOD FOR MEAS- URING DETONATION VELOCITIES IN EXPLOSIVES Thomas Q. Ciccone, Langhorne, and James F. Kowalick, Southampton, Pa., assignors to the United States of America as represented by the Secretary of the Army Filed Nov. 27, 1968, Ser. No. 779,335 Int. Cl. G01n 33/22 US. Cl. 73-35 4 Claims ABSTRACT OF THE DISCLOSURE Two lengths of explosive-detonating cord are adhesively joined together to form a double length of cord intermediate their ends. The double cord length is helically Wrapped around an elongated metallic rod and one end of each length of cord is secured to a body of explosive for initiation in response to detonation of the body. A detonator, attached to the body near one of the secured cord ends, detonates the body and initiates the cord length. Initiation fronts, travelling along the cord length, form a mark in the metallic rod where the fronts meet. The mark location relative to the cord lengths, detonation velocity of the cords and the distance between the secured ends is representative of the detonation velocity of the explosive body.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

The conduct of research and development in the ordnance art has generated an ever increasing demand for accurate and inexpensive devices for measuring detonation velocity in explosive bodies. At present, mechanical and electronic devices are used, however, they possess certain disadvantages in that, the mechanical devices are slow and extremely complicated, and the electronic devices, although accurate, involve complicated wiring and elaborate instrumentation and cannot therefore be used effectively in field operations. A relatively inexpensive method, known in the art as the dAutriche method, has been used with some degree of success. This method, which is an explosive-computational technique, does not possess the accuracy of either of the aforementioned devices and is limited to relatively large bodies of explosives.

It is, therefore, an object of this invention to provide an accurate and inexpensive device for measuring the detonation velocity of explosive bodies.

It is another object of this invention to provide a method of determining the velocity of detonation of relatively small explosive bodies which may be performed without the need for elaborate instrumentation or complex wiring.

Other objects, features and advantages will become apparent from the following specification taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an apparatus for measuring detonation velocities of explosives which embodies principles of the invention.

FIG. 2 is a side elevational view of the elongated rod of FIG. 1 after the explosive body has been detonated.

FIG. 3 is a schematic diagram showing a modified form of the invention.

An explosive body (FIG. 1), having an unknown detonation velocity, is provided with a detonator 11 which is connected thereto at one end. Detonator 11 is preferably electrically actuated by means of circuit 12 which includes a source of electrical energy 13 and electrical 3,528,280 Patented Sept. 15,, 1970 switch 14. Other types of detonators may be used however with equal facility. Two lengths of explosive-detonating cord 15 and 18 are cut from a longer length of mild detonating cord (MDC) having a flexible lead sheath around a core comprising at least .1 grain per foot of PETN explosive. Cord lengths 15 and 18 are laid side by side to form overlapping portion 17 intermediate their ends A and B respectively. MDC cord lengths 15 and 18 should be equal in order to facilitate the computations which will be more fully described later in the specification. Overlapping portion 17 of cord lengths 15 and 18 is sprayed or otherwise coated with a suitable adhesive resin to form a unitary cord length between ends A and B, and the resulting unitary cord length is helically wrapped around elongated metallic rod 16 at a pitch of approximately five turns per inch of rod length. Metallic rod 16 is preferably formed from an easily deformable material such as aluminum, however, a 1 inch diameter rod formed from cold rolled steel has been used successfully. The wrapped rod 16 is then coated with a suitable adhesive resin to securely bond MDC cord lengths 15 and 18 thereto. It should be noted that it is immaterial to the invention whether the adhesive is applied to the rod aft r the cord lengths have been warpped thereon or prior to their being wrapped.

End A of MDC cord length 15 is operatively connected to explosive body 10 at a point in close proximity with detonator 11. Various connecting devices are available which would facilitate this connection, however, whatever mechanism is used it is imperative that end A be so connected to body 10 as to be initiated in response to the detonation of the body. Cord 18 has an end B which is connected to explosive body 10 in a manner similar to that used in conjunction with end A of cord length 15. The distance between points A and B in explosive body 10 is then measured and recorded for use in subsequent computations.

The operation of the apparatus will now be described. Circuit 12 is completed by closing switch 14 and electrical energy from power supply 13 activates detonator 11. Detonator 11 detonates explosive body 10 and produces a detonation wave front therein which proceeds along body 10 intermediate point A and B. When the detonation wave front reaches point A it will produce an initiation front in MDC cord length 15 which will travel therealong around rod 16. When the detonation wave front in body 10 reaches point B it will also establish an initiation front in MDC cord length 18. These initiation fronts will travel toward each other around helically wrapped rod 16. As each wave front proceeds along overlapping portion 17 of the adjacent MDC cord length it will destroy the adjacent overlapping portion without initiating it. When the two initiation fronts meet an indentation or mark 24 (FIG. 2) will be formed in the surface of rod 16. Indentation 24 will generally take the form of a double groove with a diagonal groove therebetween; a single groove 20 being formed in the surface of rod 16 other than at the place where the initiation fronts meet. The distance along rod 16 which the initiation fronts travel before they meet at mark 24 is proportional to the velocity of detonation of explosive body 10. That is, the time required for the detonation wave front to proceed from point A to point B in explosive body 10 is proportional to the portion 17 of rod 16. Thus, the detonation velocity between points A and B may be computed according to the following formula:

LABDM e MA MB J D is the known detonation velocity of mild detonating cords and 18, L MA is the distance between point A on explosive body 10 and the mark 24 on rod 16 and L is the distance between point B on explosive body and mark 24 in the surface of rod 16. Since the detonation velocity of MDC can be highly precise with little variation (a standard deviation of less than 0.11% at 8140 meters per second), the precision with which the detonation velocity may be determined is dependent upon the accuracy achieved in measuring the distances required in the equation. Thus, it is desirable to have the difference in MDC lengths (L -L as large as possible. This is easily achieved by adjusting the cord length and the number of turns of overlapping portion 17 on rod 16. By a proper choice of MDC cord lengths, detonation velocities can be measured with standard deviations considerably less than 1%. As one skilled in the art would readily preceive, the measurement of detonation velocities in an explosive body between more than two points could be achieved by employing the modified arrangement as illustrated in FIG. 3. The construction and operation of this arrangement is similar to that of FIG. 1, thereby obviating the need for further discussion at this point.

The accuracy of the instant invention may be observed from a perusal of test results. The body of explosive used for test purposes included a one foot length of 90 grain per foot explosive-detonating cord sold under the trade name of Primacord by the Ensign-Bickford Company, Sinsburg, Conn. Two adhesively connected lengths of mild detonating cord were then helically wrapped around an elongated aluminum rod. The free ends of the wrapped cord were then inserted in the Primacord length and the distance between the inserted ends was measured and recorded. The Primacord length was then detonated and an indentation in the aluminum rod was formed, its location noted and appropriate measurements were made therefrom. Computations, made according to aforementioned mathematical formula, yielded a value for the detonation velocity of the Primacord. This value was recorded and the test repeated eight times. It was observed that the average value of the computed detonation velocity of Primacord was 6970 meters per second. This value, which had an average deviation of less than 1%, is within the limits of normal variation in the detonation velocity of commercially available Primacord. Thus, it can be seen that this apparatus provides an accurate, simple and inexpensive method for measuring the detonation velocities in explosive bodies.

Various modifications, alternations or changes may be resorted to without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. An apparatus for measuring the detonation velocity of an explosive body comprising,

a surface for supporting lengths of preselected explosive-detonating cord,

a first length of explosive-detonating cord of preselected detonation velocity having one end thereof securable to said body for initiation in response to detonation of said body, said first length extending outwardly of said body and having a portion positioned on said surface,

a second length of explosive-detonating cord of preselected detonation velocity having a portion positioned on said surface adjacent to and in intimate contact with said first length portion to form a collateral extension therealong, said second length also having one end thereof securable to said body a predetermined spaced distance from said first length securable end for initiation in response to detonation of said body, and means for detonating said body adjacent said first length securable end,

whereby said body initiates said first length upon detonation of said body and said second length subsequent thereto, each of said initiated lengths having an initiation front which travels therealong to form a mark in said surface where said initiation fronts meet, such that said mark will have a location relative to said cord lengths and said predetermined spaced distance between said securable ends which is representative of said detonation velocity. 2. The apparatus of claim 1 wherein said surface is an adhesively coated metallic rod and said cord lengths are formed from mild detonating cord having an explosive core with a flexible lead sheath, said core comprising at least .1 grain per foot of PETN explosive.

3. The apparatus as defined in claim 2 wherein said .metallic rod is aluminum.

4. The method of measuring the detonation velocity of an explosive comprising the steps of:

selecting an explosive body, placing first and second predetermined lengths of an explosive-detonating cord having a preselected detonation velocity in adjacent relationship on an adhesively coated metallic supporting surface,

securing one end of said first length to said body for initiation of said cord in a predetermined direction outwardly of said body in response to detonation of of said body,

securing one end of said second length to said body a measured predetermined distance from the secured end of said first length, said second length being initiated in a direction outwardly of said body and opposite to the initiation direction of said first length in response to the detonation of said body,

marking the location of the secured ends to establish measuring reference points,

detonating said body of explosive adjacent the secured end of one of said lengths, whereby initiation fronts are produced in said lengths and a discernable indentation is formed in said surface where said initiation fronts meet,

measuring said indentation location relative to said reference points, and

computing the detonation velocity of said explosive body according to the formula:

where D is the detonation velocity of said explosive body, L is a predetermined measured distance between said secured ends, L is a distance between said indentation and said first cord length secured end, and L is the distance between said indentation and said second cord length secured end.

References Cited UNITED STATES PATENTS 3,408,855 11/1968 Slykhouse 73--35 JAMES J. GILL, Primary Examiner H. GOLDSTEIN, Assistant Examiner 

